1. Field of the Invention
The invention relates to a heel-piece for a safety ski binding, the heel-piece being released when a specific load exerted on the binding is exceeded. A link mechanism is provided between the sole-holder and the binding plate of the ski, the link mechanism including two pivot pins, which in the operational position of the heel-piece, are transverse to the ski and parallel to its surface. The sole-holder is connected by the link mechanism, including the pivot pins, to the binding plate. The sole-holder and the binding plate are mutually engaged by a spring-loaded detent and detent-track.
2. Description of the Related Art
German Offenlegungsschrift No. 31 07 230 discloses a heel-piece comprising a carriage displaceable essentially transversely to the longitudinal axis of the ski and held in its center position by a spring-loaded detent-track and a detent snapping into the detent-track. This carriage is operationally displaceable relative to the ski upon suitable torques exerted on the heel-piece and supports a pivoting link mechanism within which is held a release mechanism. The link mechanism is locked by an elbow lever hingedly connected at its ends to the carriage and to the link mechanism. A pivoting lever is pivotably fastened on the carriage and is received in a groove of a base plate fixed to the ski. The pivot lever blocks the elbow of the elbow lever at the center of the excursion of the carriage and releases the elbow the moment the carriage has been displaced from the center, whereby the link mechanism and hence the release mechanism can be swung upwardly.
This arrangement has the disadvantage of being cumbersome and costly in design. Moreover, it fails to provide compensation for minor changes in the length of the sole of the boot held by the heel-piece, or compensation for a layer of snow on the sole, even if relatively slight.
Also, WO No. 84/03050 discloses a heel-piece of the type discussed above. In this heel-piece the sole-holder is connected by an elbow lever to the binding plate of a ski and rests at its center pivot point on a spring-loaded lever with a detent-track. Further, the sole holder is connected by a double lever to the binding plate. A link mechanism is held on the binding plate and intersects the double lever, which further pivots at one of its ends on the sole holder. Because the two hinge points of the sole-holder are comparatively close to each other, and because the part of the elbow lever and of the double lever pivoting on the hinge points are of different lengths, the longitudinal displacement of the ski binding entails a very complex motion of the sole holder, during which the spacing between the fastening strip of the sole-holder and the surface of the ski changes. As a result, the compression of the boot on the ski varies considerably and thereby increases the frictional forces to be overcome to release the ski binding in the event of a twisting fall. Therefore, the snow layers adhering to the vertical surfaces in the toe and the heel areas of the boot will also affect the release.
It is an object of the present invention to avoid these drawbacks and to provide a heel-piece which is characterized by a simple design which allows for length compensation, thereby compensating for snow layers on the sole in the absence of significant variations in the release values. This object is achieved in the present invention by connecting the sole-holder to the binding plate by only the link mechanism and by connecting one of the components of the detent/detent-track to one of the binding plate and the sole-holder and by connecting the other component to the other of the binding plate and the sole holder. The detent-track slants in a known manner relative to the ski topside, and the detent and the detent-track engage each other. Because only one pivoting connection is present between the sole-holder and the binding plate, namely the pivot pins of the link mechanism, a longitudinal displacement of the sole-holder relative to the binding plate produces practically no change in boot pressure on the ski. Despite the resulting compression of the compression spring of the detent mechanism of the detent mechanism, the set released values therefore remain substantially constant.
For the sake of simplicity of design, the link mechanism is mounted on the end of the sole-holder opposite the toe piece and is substantially vertical in the operational position of the heel-piece. Even if the link mechanism is comparatively short, it may nevertheless compensate length changes in the sole, and this is significant in particular for soles made of hygroscopic materials.
It is preferable that the detent-track of the present invention is pivotably mounted on a pivot arm fastened to the binding plate. It is further preferable that the detent comprises a roller rotatably supported on a sole-holder, the arm resting on a compression spring, which, in turn rests on a support controlled by a release mechanism. By means of this arrangement, the opening of the heel-piece caused by the sole-holder pivoting upwardly following release is covered by the pivot arm with the detent-track, whereby, in the event of a fall, no snow may enter the inside of the heel-piece. As a result, heel-piece malfunctions are often averted.
According to another feature of the present invention, the abutment controlled by the release mechamism comprises a support arm pivotably fastened to the binding plate and a snap-in arm which supports the support arm in the operational position. The support arm is pivotally connected to the pivot arm by a coupling rod guiding the compression spring and loads, in a known manner, the snap-in arm in its longitudinal direction. The compression spring is preferably substantially parallel to the ski surface. This arrangement provides the advantage that the snap-in arm can be displaced by relatively small forces from the position where it supports the support arm, whereby the snap-in arm, along with the compression spring, loses its support. Thereby, the sole-holder is unlocked from the binding plate. The support of the compression spring by the coupling rod is essential in this regard to avert stretching of the spring, which unevenly stretches it and causes premature fatigue.
Basically, the heel-piece of the invention is applicable both to a detachable toe piece and a non-detachable toe piece, which is frequently used in cross-country bindings. However, for reasons for high-release reliability, it will be appropriate when using the heel-piece of the invention together with a non-detachable toe piece that the heel-piece be used together with a binding plate. Thus, according to a further feature of the present invention, the heel-piece includes a binding plate fixed to the ski and pivotable about a vertical pivot boss located at the intersection of the tibia axis of the skier and the plane of the ski, and further about a pivot pin located in the front of the binding plate, transverse to the ski's longitudinal axis. The pivot boss is secured against rotation by a vertical pin or detector spaced from the pivot boss and received in a support fixed in the ski.
According to a further aspect of the invention, the detector preferably is connected by a transducer to the binding plate. This feature is especially suitable for heel-pieces with an electronically controlled release mechanism so that the forces acting on the binding can be sensed over very short distances. With this arrangement, any slight displacement of the plate relative to the ski is determined by the elasticity of the individual components of the plate, as well as the fastening of the binding plate on the ski, is sufficient to detect the applied forces. It is preferable that the transducer is mounted in a tightly sealed housing in which are located in electronic circuit analyzing the transducer output signals and a setting member controlling the snap-in arm. With this arrangement, short transmission paths are achieved for the transducer output signals and the highly sensitive electronic components are protected.
Additional objects and the advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the dependent claims.